Since 1987, the swine-producing industry has been subjected to a devastating epidemic of an unknown disease, often referred to as xe2x80x9cMystery Swine Diseasexe2x80x9d [MSD, more recently referred to as xe2x80x9cSwine Infertility and Respiratory Syndrome (SIRS)], because researchers have been unable to identify the causative agent. MSD has affected hundreds of thousands of swine throughout North America and Europe.
Once one pig is infected with MSD, that one pig can spread the MSD to an entire herd within three to seven days. From 1987 to 1991, the swine industry has lost millions of dollars in revenue as a result of MSD. A recent study estimates that MSD causes a financial loss between $250 and $500 per inventoried sow.
MSD causes multiple symptoms in swine. The first symptom of MSD in a breeding herd of swine is usually anorexia and mild pyrexia. In addition, the herd animals may exhibit bluish discolorations in their skin, especially in their ears, teats, snout, and the frontal portions of their necks and shoulders. The affected skin may become irreparably damaged. However, the most devastating symptom of MSD is the reproductive failure that occurs in a breeding herd of swine. MSD causes sows to bear stillborn piglets; undersized, weak piglets with respiratory distress; or piglets which die before they are weaned. Other reproductive symptoms caused by MSD include early farrowing of piglets, a decrease in conception rates, failure in some sows to cycle, and a reduction in the total number of piglets found in a litter. It has been estimated that the number of pigs lost from reproductive failure is about 10 to 15 percent of the annual production of pigs.
Research has been directed toward isolating the causative agent of MSD. A number of potential bacterial pathogens have been isolated. However, the types of potential bacterial pathogens have varied between swine- producing farms. Viral investigation has included fluorescent antibody examination, electron microscopic investigation, and serology. These methods have failed to locate the causative agent of MSD. As a result, no one has yet developed a vaccine which can be used to treat MSD in the swine population.
Therefore, it is an objective of the invention to provide a vaccine and sera which, when administered to a breeding swine herd, will reduce the presence of MSD in their population. Another object is to provide a method of treating a population of swine with the vaccine to eradicate MSD from the swine population. Yet another object is to provide a method for diagnosis of MSD.
These and other objects are achieved by the present invention which is directed to a vaccine and sera for prevention and treatment of mystery swine disease and to a method for its diagnosis in swine.
The vaccine is derived from an infectious agent that will infect swine with mystery swine disease (MSD). The infectious agent is obtained from an inoculum of processed tissue of swine infected with the disease, preferably lung tissue. Preferably, the infectious agent is the product of an in vitro mammalian cell culture such as a simian cell line infected with the inoculum of the infected swine tissue. Preferably, the inoculum contains biological particles no greater than about 1.0 micron in size, more preferably 0.5 micron, most preferably no greater than 0.2 micron. It is also preferable that the inoculum has been neutralized with antibodies to common swine diseases.
According to the present invention, a tissue homogenate obtained from piglets in SIRS-affected herds consistently reproduced the respiratory and reproductive forms of SIRS when intranasally inoculated in gnotobiotic piglets and pregnant sows. Gnotobiotic piglets so inoculated with-either unfiltered or filtered (0.45, 0.22, or 0.1 xcexcm) inoculum became anorectic and developed microscopic lung lesions similar to lesions seen in SIRS-affected herds. The same inoculum also caused reproductive effects identical to those seen in SIRS-affected herds. A viral agent has been recovered from the tissue homogenate. The viral agent causes a disease that mimics SIRS in piglets and pregnant sows. The viral agent has not yet been classified. However, the viral agent is a fastidious, non-hemagglutinating enveloped RNA virus. A viral agent causing SIRS has been deposited on Jul. 18, 1991 with the American Type Culture Collection 12301 Parklawn Dr. Rockville, Md. 20852 under the accession number ATCC VR-2332.
The serum for treatment of infected swine carries mammalian antibodies to the MSD. It is obtained from the blood plasma of a mammal (non-swine and swine) pre-treated with the above-described infectious agent.
Alternatively, the serum is formulated from monoclonal antibodies to MSD produced by hybridoma methods. The method for diagnosis of MSD is based upon the use of immunospecific antibodies for MSD. The method calls for combination of a filtered homogenate of a lung biopsy sample or a biopsy sample or similar samples (homogenate or biopsy) from other tissue and the immunospecific antibodies followed by application of a known detection technique for the conjugate formed by this combination. Immobilization or precipitation of the conjugate and application of such detection techniques as ELISA; RIA; Southern, Northern, Western Blots and the like will diagnose MSD.
According to the present invention, therapeutic and diagnostic methods employing antibodies to MSD involve monoclonal antibodies (e.g., IgG or IgM) to the above-described fastidious, non-hemagglutinating enveloped RNA virus. Exemplary antibodies include SDOW 12 and SDOW 17, deposited with the American Type Culture Collection on Mar. 27, 1992 with accession numbers HB 10996 and HB 10997, respectively).